The next screen will appear after you enter the key and is the standard license terms for pre-release software. Once you accept the term and hit next you will then be given the option for different installations.
You can’t do an upgrade by booting from the ISO image if you wanted to do that you would have to be booted into version of windows you wanted to upgrade from. So click custom and you will be presented with a drive selection screen.
Since we have only one drive to choose from, it is ok to go ahead and click next to start the installation process which will look like this.